ᐅ CO2 as an Insulating Gas in Windows?

Hello everyone,

thanks in advance for your help, and I hope this is the right subforum for my question.
Since I want to run ventilation through a window, I made a double pane out of plexiglass (with two openings for the ventilation pipes) that I insert into the frame instead of the window. However, I have recently realized that this might not be ideal in terms of insulation. Therefore, I considered whether filling the space between the panes with gas would help (so far it's only air, dehumidified by silica gel in the PVC profile between the panes). Argon is relatively affordable in small quantities, but even cheaper would be carbon dioxide from the kitchen soda maker.
Unfortunately, I haven’t found any information on why CO2 isn’t used as a fill gas in windows, even though it has a similar thermal conductivity to argon. Would this make sense, and can the gas (regardless of which one) actually be retained—the panes are sealed with silicone?

Fabian12 schrieb:

Would that make sense, and would the gas (regardless of type) actually be retained – the panes are sealed with silicone?

My first big question is: How do you get the gas into the glass without any “normal” air getting in?

I would suggest proper ventilation through a core drilling next to the window (if there is space). I strongly assume that, as a layperson, you won’t be able to install a proper window with insulation glazing performance comparable to standard double glazing.

A key factor with glazing is the thermal insulation in modern windows compared to the insulated glazing used until the mid-1990s. The glass is coated with a layer that reflects infrared radiation. This reduces the U-value from 3 to 1. The gas filling is only of secondary importance or relevant just for the first decimal place.
You can’t achieve this with plexiglass.

Thank you for the responses. I understand that I can't compare this with modern thermal insulation glazing. The benchmark would rather be the installed windows. Since the house was built in the mid-1990s, I am honestly not sure if thermal insulation glass was already used then. The lighter test was not really conclusive...

This is roughly how I imagined filling it: drill a small hole at the top and bottom, fill with gas from the bottom (or flush long enough), and seal both holes with silicone (?)